Conventionally, control that reduces a current leaking to a ground is executed in an electric-motor driving device that drives an electric motor. For example, Patent Literature 1 listed below discloses a technique that, in an anti-phase voltage generating unit, stores in advance correction table data obtained by adjusting a phase and an amplitude of an anti-phase voltage so as to minimize a leak current, together with sine-wave table data in a memory, and injects a current canceling out the leak current to a power-supply ground point.
Also, Patent Literature 2 listed below discloses a technique in which a table for selecting a duty of PWM (Pulse Width Modulation) control of a leak-reduction driving unit is provided in a leak-current canceller circuit.
Further, Patent Literature 3 listed below discloses a technique that, in an inverter device, obtains an accurate current flowing in an alternating-current electric motor by detecting a leak current flowing to the earth via a floating capacitance in advance, storing the detected leak current in a storing circuit, and subtracting the leak current in the storing circuit from a detected current flowing in the alternating-current electric motor.
In addition, Patent Literature 4 listed below discloses a technique that, in a compressor driving device of an air conditioner, a leak current that is a zero-phase current is detected by a common mode coil, and an anti-phase current is injected to a housing ground point in such a manner that the detected current is canceled out, so that compensation to make the leak current zero is achieved.